Superparamagnetic fluids and methods of making superparamagnetic fluids are well known in the art and are generally described in Wyman U.S. Pat. Nos. 4,430,239, 4,701,276 and 4,741,850, which are incorporated herein in their entirety. The uses and applications for superparamagnetic fluids are also set forth in these references.
As described in U.S. Pat. No. 4,701,276, a magnetic fluid includes a carrier liquid, a dispersing agent which is a salt of an aromatic sulfonic acid for dispersing coated magnetic particles in the carrier liquid, and magnetic particles coated with at least one organic acid which renders the magnetic particles hydrophobic and which peptizes the magnetic particles into a fugitive carrier liquid which is a solvent for a dispersing agent.
Therefore, formation of the magnetic colloids discussed in U.S. Pat. No. 4,701,276 requires two dispersants, namely a dispersing agent and an organic acid. The organic acid must peptize the magnetic particles into a fugitive carrier which is a solvent for the dispersing agent. Moreover, this method of making a magnetic colloid is unduly complicated because of the additional steps necessitated by the requirement of both a dispersing agent and an organic acid to form stable magnetic colloids.
The present invention provides stable magnetic colloids which are easily produced and which do not require both a dispersing agent and an organic acid.